pthread_rwlock_init.c 2.6 KB

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  1. /* Copyright (C) 2002, 2007, 2009 Free Software Foundation, Inc.
  2. This file is part of the GNU C Library.
  3. Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
  4. The GNU C Library is free software; you can redistribute it and/or
  5. modify it under the terms of the GNU Lesser General Public
  6. License as published by the Free Software Foundation; either
  7. version 2.1 of the License, or (at your option) any later version.
  8. The GNU C Library is distributed in the hope that it will be useful,
  9. but WITHOUT ANY WARRANTY; without even the implied warranty of
  10. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  11. Lesser General Public License for more details.
  12. You should have received a copy of the GNU Lesser General Public
  13. License along with the GNU C Library; if not, write to the Free
  14. Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  15. 02111-1307 USA. */
  16. #include "pthreadP.h"
  17. #include <bits/kernel-features.h>
  18. static const struct pthread_rwlockattr default_attr =
  19. {
  20. .lockkind = PTHREAD_RWLOCK_DEFAULT_NP,
  21. .pshared = PTHREAD_PROCESS_PRIVATE
  22. };
  23. int
  24. __pthread_rwlock_init (
  25. pthread_rwlock_t *rwlock,
  26. const pthread_rwlockattr_t *attr)
  27. {
  28. const struct pthread_rwlockattr *iattr;
  29. iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_attr;
  30. memset (rwlock, '\0', sizeof (*rwlock));
  31. rwlock->__data.__flags
  32. = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
  33. /* The __SHARED field is computed to minimize the work that needs to
  34. be done while handling the futex. There are two inputs: the
  35. availability of private futexes and whether the rwlock is shared
  36. or private. Unfortunately the value of a private rwlock is
  37. fixed: it must be zero. The PRIVATE_FUTEX flag has the value
  38. 0x80 in case private futexes are available and zero otherwise.
  39. This leads to the following table:
  40. | pshared | result
  41. | shared private | shared private |
  42. ------------+-----------------+-----------------+
  43. !avail 0 | 0 0 | 0 0 |
  44. avail 0x80 | 0x80 0 | 0 0x80 |
  45. If the pshared value is in locking functions XORed with avail
  46. we get the expected result. */
  47. #ifdef __ASSUME_PRIVATE_FUTEX
  48. rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
  49. ? 0 : FUTEX_PRIVATE_FLAG);
  50. #else
  51. rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
  52. ? 0
  53. : THREAD_GETMEM (THREAD_SELF,
  54. header.private_futex));
  55. #endif
  56. return 0;
  57. }
  58. strong_alias (__pthread_rwlock_init, pthread_rwlock_init)